EAS system loop antenna having three loops of different area

Abstract

An EAS system in which a transmitter alternately drives first and second antennas with the same coded message signal in its entirety. The antennas, in turn, transmit first and second signals each containing the coded message signal into respective first and second partially overlapping parts of an interrogation zone. Also disclosed is an antenna structure comprised of a plurality of loops extending one after the other and successive ones of which are of opposite phase. One of the loops circumscribes an area which is smaller than each of the other loops to realize reduced coupling to adjacent structures.

What is claimed is 
     
       1. An antenna for use with an EAS system, said antenna comprising: first, second and third loops, said first, second and third loops being coplanar and being arranged one after the other along a common axis and such that successive loops are of opposite phase, said second loop being situated between said first and third loops;   said first loop including: a first horizontal loop segment; second and third vertical loop segments extending from opposite ends of said first loop segment; fourth and fifth loop segments, said fourth loop segment extending from said second loop segment at an acute angle of less than about 45° relative to the vertical direction and in the direction of said third loop segment, said fifth loop segment extending from said third loop segment at an acute angle of less than about 45° relative to the vertical direction and in the direction of said second loop segment, said fourth and fifth loop segments extending to a first intersection point;   said second loop including: sixth and seventh loop segments, said sixth loop segment extending from said fourth loop segment and being inclined at an acute angle of less than about 45° relative to the vertical direction and said seventh loop segment extending from said fifth loop segment and being inclined at an acute angle of less than about 45° relative to the vertical direction; eighth and ninth vertical loop segments extending from said sixth and seventh loop segments, respectively; tenth and eleventh loop segments, said tenth loop segment extending from said eighth loop segment and being inclined at an acute angle relative to the vertical direction and in the direction of said ninth loop segment, said eleventh loop segment extending from said ninth loop segment and being inclined at an acute angle relative to the vertical direction and in the direction of said eighth loop segment, said tenth and eleventh loop segments extending to a second intersection point;   said third loop including: twelfth and thirteenth loop segments, said twelfth loop segment extending from said eleventh loop segment and being inclined at an acute angle relative to the vertical direction and said thirteenth loop segment extending from said tenth loop segment and being inclined at an acute angle relative to the vertical direction; fourteenth and fifteenth loop segments extending vertically from said twelfth and thirteenth loop segments, respectively; and a sixteenth loop segment extending horizontally between said fourteenth and fifteenth loop segments.   
     
     
       2. An antenna in accordance with claim 1 wherein: said third loop circumscribes an area which is less than the area circumscribed by each of said first and second loops.   
     
     
       3. An antenna in accordance with claim 2 wherein: each of said first, second and third loops is asymmetric relative to a horizontal line drawn through said each loop.   
     
     
       4. An antenna in accordance with claim 2 wherein said first loop circumscribes an area which is less than the area circumscribed by said second loop. 
     
     
       5. An antenna in accordance with claim 1 wherein: the acute angle made by each of said fourth and fifth loop segments relative to the vertical direction is at a first angle;   and the acute angle made by each of said sixth and seventh loop segments relative to the vertical direction is at a second angle different from said first angle.   
     
     
       6. An antenna in accordance with claim 5 wherein: said second angle is smaller than said first angle.   
     
     
       7. An antenna in accordance with claim 6 wherein: the acute angle made by each of said tenth, eleventh, twelfth and thirteenth loop segments is greater than said first angle.   
     
     
       8. An antenna in accordance with claim   7 wherein: the acute angle made by each of said tenth, eleventh, twelfth and thirteenth loop segments is substantially greater than each of said first and second angles and less than about 45°.   
     
     
       9. An antenna in accordance with claim 1 wherein: the vertical length covered by the fourth and sixth loop segments and the fifth and seventh loop segments is moderately large relative to the overall vertical length of said first, second and third loops.   
     
     
       10. An antenna in accordance with claim 9 wherein: the vertical length covered by the eleventh and twelfth loop segments and the tenth and thirteenth loop segments is small relative to the overall vertical length of said first, second and third loops.   
     
     
       11. An antenna in accordance with claim 1 wherein: said antenna is formed from a continuous cable which has been criss-crossed to define said first, second and third loops.